1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a power transmission belt having a cloth component applied over a surface on which teeth are formed.
2. Background Art
Toothed power transmission belts with a cloth component thereon are used in a number of different environments under conditions that are often relatively severe. For example, toothed belts are used to drive components on automobile engines, such as a cam shaft, an injection pump, an oil pump, a water pump, and the like. Since automobile engine compartments are increasingly becoming more compact, these belts are required to operate in environments at elevated temperatures generated during engine operation. The environmental conditions and loads encountered dictate the need for toothed belts with higher durability.
These toothed belts are also used on rear-wheel drives of large, high-powered motorcycles, increasingly in place of chain and sprocket drives that have been used in the past.
These toothed belts are used also on industrial machinery as, for example, on injection molding equipment. In this environment, the belts may be subjected to high loads and may be required to operate for long periods without replacement.
Toothed belts are used in other environments in which they are commonly subjected to severe loading and environmental conditions that tend to lead to premature failure.
To avoid premature failure, improvements have been made on toothed belts in a number of different areas. The materials of load carrying members that extend lengthwise of the belts have been changed for improved durability and longevity. Thinner load carrying members have also been developed. Further, treating agents for load carrying cords have been devised to improve the heat resistance thereof. These improvements have been focused on avoiding failure due to flexing fatigue of the load carrying members as well as inadequate heat resistance of the rubber in which they are embedded. Additionally, hydrogenated nitrile rubber has been used to improve heat resistance, thereby decreasing the likelihood of premature failure.
Toothed belts used on engines in which the belts are highly loaded, and in driving industrial machinery, are often abraded to a significant degree at the base portion of the teeth. It is also common for the teeth to chip as a result of abrasion at the base portion of the teeth.
Additionally, under high loads, pulley shafts tend to bend, whereby the travelling path defined by the pulley tends to skew. When this occurs, the belt does not properly seat in the pulleys and runs at an angle with respect thereto, as a result of which there is a tendency for there to be abnormal abrasion at the belt side surfaces that contact the cooperating pulley flanges. Cutting and chipping of the teeth at the side surfaces may occur with this operating condition.
In a high load application, the belts also tend to stretch to an extent that an autotensioner does not effectively make compensation. As a result, the belt may not be properly tensioned whereupon operation of associated mechanisms, such as an engine or accessories thereon, may not operate consistently or normally.
To counter abrasion of the belt side surfaces, and damaging elongation of a belt, it is known to use a fluorine resin that tends to reduce the coefficient of friction of the associated surface. It is also known to apply a layered graphite, or the like, to a cloth composition on the tooth surfaces that mesh with a cooperating pulley. Generally, it is believed that these steps do not account for adequate improvement, particularly with respect to load carrying member performance.
In JP-B-58-334323, a cloth component for a toothed belt is disclosed with separate yarns. In one of the yarns, 6-nylon or 6, 6-nylon fiber material is used for purposes of good adhesion with rubber. In the other yarn, fluorine fibers or carbon fibers are used. The dimensional accuracy of the toothed portion of the belt may not be maintainable merely using fluorine fibers or carbon fibers in the yarns. A product with this cloth component may not be useable in the automotive environment in which a high, maintained level of dimensional accuracy of the tooth region is required.